"We are not winning in Afghanistan right now. And we will correct this as soon as possible," Mattis said during a congressional hearing.

In a candid admission, US Defence Secretary Jim Mattis on Tuesday said that the United States is still "not winning" the longest war in Afghanistan.

However, he added that the US will try to correct it as soon as possible.

"We are not winning in Afghanistan right now. And we will correct this as soon as possible," Mattis said during a congressional hearing.

According to Mattis, the Pentagon defines the winning in Afghanistan as a situation where the Afghan government, with international help, would be able to handle the violence and drive it down to a level that local security forces can handle it.

"It would probably require residual force doing training and maintaining the high-end capability," said Mattis. "It's going to be an era of frequent skirmishing and it's going to require a change in our approach from the last several years if we're to get it to that position."

Mattis was not the first senior official of the administration of U.S. President Donald Trump to publicly warn of a dire prospect for the security situation in Afghanistan.

US National Intelligence Director Dan Coats also warned last month that the security situation in Afghanistan would most likely deteriorate in the future even if the United States and its allies offer more military aid.

The warnings came as Trump was reportedly considering whether or not to send additional hundreds of US troops to Afghanistan.

Former US President Barack Obama had planned to reduce the current number of 9,800 US troops in Afghanistan to some 5,500 by the end of 2015 and withdraw all troops by the end of 2016 when his presidency came to an end.

However, given the deteriorating security situation in Afghanistan, the Obama administration repeatedly postponed the withdrawal.

Currently, there are about 8,400 US troops and another 5,000 forces of the North Atlantic Treaty Organization (NATO) on the ground in Afghanistan to train and assist the Afghan forces against the Taliban, and conduct counter-terrorism missions.